1. Field of the Invention
The stimulation of cardiac tissue using an acoustic transducer, referred to as a controller-transmitter, and one or more implanted receiver-stimulator devices has recently been proposed by the inventors herein in the patent applications referred to above. The controller-transmitter produces an acoustic signal which is received by the receiver-stimulator, and the receiver-stimulator in turn generates an electrical signal which is delivered to cardiac or other tissue through coupled tissue electrodes. The controller-transmitter may be external, but will usually be implanted, requiring that the controller-transmitter have a reasonable size, similar to that of implantable pacemakers, and that the controller-transmitter be capable of operating from batteries for a lengthy period, typically three or more years. The relatively small size and relatively long operational period require that the receiver-stimulators efficiently utilize the acoustic energy from the controller-transmitters.
For those reasons, it would be desirable to provide implantable transducer devices which are able to efficiently receive acoustic energy from implanted or external acoustic transmitters. It would be particularly desirable if the transducers could operate in an isotropic or nearly isotropic fashion where they could efficiently receive acoustic energy from an acoustic transmitter regardless of the relative orientation between the transmitter and the implanted transducer. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
The following patents and patent publications describe various implantable transducers capable of converting applied acoustic energy into an electrical output: U.S. Pat. Nos. 3,659,615; 3,735,756; 5,193,539; 6,654,638; 6,628,989; and 6,764,446; U.S. Patent Application Publications 2002/0077673; 2004/0172083; and 2004/0204744; and published German application DE 4330680.